A wireless system in which transmit data is divided into in-phase (I) and quadrature (Q) components and radio frequency (RF) quadrature modulated signals are generated by modulating carriers which are 90 degrees out of phase with each other by these I and Q components is used for mobile phones or the like. In a receiver for use in such wireless system, instead of a heterodyne system in which RF signals are once converted into intermediate frequency (hereinafter abbreviated to IF) signals and the IF signals are demodulated into I and Q signals, a direct conversion system in which received signals (RF quadrature modulated signals) are directly demodulated into I and Q signals, which is known as a zero-IF system, has been put into use. Because the zero-IF system dispenses with IF amplification and filtering, the receiver with fewer components than when using the heterodyne system can be constructed. The zero-IF system can contribute to downsizing and cost reduction which are strongly required for wireless devices.
In the zero-IF system, however, phase mismatch and amplitude mismatch between I and Q signals are liable to occur and these mismatches are liable to result in bit errors in demodulated data. To avoid this problem, a demodulator arranged to detect I-Q phase and amplitude mismatches and correct these mismatches, using detection results, is disclosed in JP-A No. 2004-40678.